[PATCH] selftests/mm: fix khugepaged_race build with older glibc

[Zenghui Yu <zenghui.yu@linux.dev>]

From: "Zenghui Yu (Huawei)" <zenghui.yu@linux.dev>

glibc versions before 2.37 do not define MADV_COLLAPSE in <sys/mman.h>, so
khugepaged_race fails to build against them (e.g. glibc 2.34):

[root@localhost mm]# make
  CC       khugepaged_race
khugepaged_race.c: In function 'main':
khugepaged_race.c:506:23: error: 'MADV_COLLAPSE' undeclared (first use in this function); did you mean 'MADV_COLD'?
  506 |       hpage_pmd_size, MADV_COLLAPSE);
      |                       ^~~~~~~~~~~~~
      |                       MADV_COLD
khugepaged_race.c:506:23: note: each undeclared identifier is reported only once for each function it appears in
make: *** [../lib.mk:225: /data/code/mm/tools/testing/selftests/mm/khugepaged_race] Error 1

Include <linux/mman.h> to get the UAPI definition of MADV_COLLAPSE.

Fixes: 66c374464438 ("selftests/mm: add khugepaged race harness")
Signed-off-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
---
 tools/testing/selftests/mm/khugepaged_race.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index abb0678522cd..1a27cb39745b 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -8,6 +8,7 @@
 #define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
+#include <linux/mman.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
-- 
2.56.0